1. Field of the Invention
The present invention relates to a mechanism for moving a running member on a track plate having a guide means in forward, rearward, leftward, and rightward directions.
2. Description of the Prior Art
A moving mechanism of a running member shown in FIG. 7 is known as a prior art. In this mechanism, a running member 2 is disposed on a track plate 1 having a plurality of guide grooves 1a.
The moving mechanism of the running member 2 comprises a drive wheel 4 and sprockets 6 and 6. The drive wheel 4 is rotated by a motor 3 that serves as a drive means through a reduction gear (not shown) so as to move the running member 2 in a forward direction (in which the guide grooves extend). The sprockets 6 and 6 are engaged with the guide grooves 1a on the track plate 1 so as to move the running member 2 in leftward and rightward directions.
The drive wheel 4 comprises two divided wheels 4a and 4b. Rubber belts 4c and 4d are disposed on the outer peripheries of the divided wheels 4a and 4b, respectively. The divided wheels 4a and 4b are pivoted by support shafts 7 and 7, respectively. Thus, the divided wheels 4a and 4b are slidable along the respective support shafts 7 and 7.
While the rubber belts 4c or 4d of the divided wheel 4a or 4b is in contact with the track plate 1, when the running member 2 is moved in the leftward or rightward direction by the rotations of the sprockets 6 and 6, the divided wheel 4a or 4b is moved in the rightward or leftward direction on the support shaft 7.
Thus, while the running member 2 is being moved in forward direction by the drive wheel 4, it can be moved in the leftward and rightward directions by the sprockets 6 and 6. Consequently, the running member 2 can be moved in an oblique direction.
An example of this type of mechanism is disclosed in Japanese Patent Laid-Open Publication No. Hei 2-92383.
[Problem to be solved by the Invention]
However, in such a conventional mechanism, the frictional coefficient between the track plate 1 and the rubber belts 4c and 4d lowers due to aged deterioration of the rubber belts 4c and 4d. In addition, since frictional force takes place between the sprockets 6 and 6 and the guide grooves 1a of the track plate 1 while the running member 2 is going in the oblique direction, the drive wheel 4 slips. Thus, the moving distance of the running member 2 does not accord with the rotation of the drive wheel 4. Thus, the accuracy of the moving distance is low.
In addition, when the running member 2 is moved in the oblique direction by the rotations of the sprockets 6 and 6, the divided wheel 4a or 4b of the drive wheel 4 is slidably moved to the right or left on the support shaft 7. Thus, a sliding resistance takes place between the divided wheel 4a or 4b and the support shaft 7. Consequently, when the running member 2 is moved in the oblique direction, a useless load caused by the frictional resistance is applied to the motor 5.